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Is it possible to store a regex match and use part of it as a list enumerator?

I have created a MadLibs style game where the user enters responses to prompts which in turn replace blanks, represented by %s0, %s1 etc., in a story. I have this working using a for loop but someone else suggested I could do it using regex. What I have so far is below, which replaces all instances of %s+number with "wibble". What I was wondering is if it is possible to store the number found by the regex in a temporary variable and in turn use that to return a value from the list Words? E.g. return Regex.Replace(story, pattern, Global.Words[x]); where x is the number returned by the regex pattern as it goes over the string.
static void Main(string[] args)
{
Globals.Words = new List<string>();
Globals.Words.Add("nathan");
Globals.Words.Add("bob");
var text = "Once upon a time there was a %s0 and it was %s1";
Console.WriteLine(FindEscapeCharacters(text));
}
public static string FindEscapeCharacters(string story)
{
var pattern = #"%s([0-9]+)";
return Regex.Replace(story, "%s([0-9]+)", "wibble");
}
Thanks in advance, Nathan.

Not a direct answer to your question about regexes, but if I understand you correctly, there is an easier way to do this:
string baseString = "I have a {0} {1} in my {0} {2}.";
List<string> words = new List<string>() { "red", "cat", "hat" };
string outputString = String.Format(baseString, words.ToArray());
outputString will be I have a red cat in my red hat..
Is that not what you want, or is there more to your question that I'm missing?
Minor elaboration
String.Format uses the following signature:
string Format(string format, params object[] values)
The neat thing about params is that you can either list values separately:
var a = String.Format("...", valueA, valueB, valueC);
but you can also pass in an array directly:
var a = String.Format("...", valueArray);
Note that you can't mix and match the two approaches.

Yes, you are very close in your attempt with Regex.Replace; the last step is to change constant "wibble" into lambda match => how_to_replace_the_match:
var text = "Once upon a time there was a %s0 and it was %s1";
// Once upon a time there was a nathan and it was bob
var result = Regex.Replace(
text,
"%s([0-9]+)",
match => Globals.Words[int.Parse(match.Groups[1].Value)]);
Edit: In case you don't want working with capturing groups by their numbers, you can name them explicitly:
// Once upon a time there was a nathan and it was bob
var result = Regex.Replace(
text,
"%s(?<number>[0-9]+)",
match => Globals.Words[int.Parse(match.Groups["number"].Value)]);

There is an overload of Regex.Replace that, rather than taking a string for the last argument, takes a MatchEvaluator delegate - a function that takes a Match object and returns a string.
You could make that function parse the integer from the Match's Groups[1].Value property and then use that to index into your list, returning the string you find.

Split string with plus sign as a delimiter

I have an issue with a string containing the plus sign (+).
I want to split that string (or if there is some other way to solve my problem)
string ColumnPlusLevel = "+-J10+-J10+-J10+-J10+-J10";
string strpluslevel = "";
strpluslevel = ColumnPlusLevel;
string[] strpluslevel_lines = Regex.Split(strpluslevel, "+");
foreach (string line in strpluslevel_lines)
{
MessageBox.Show(line);
strpluslevel_summa = strpluslevel_summa + line;
}
MessageBox.Show(strpluslevel_summa, "summa sumarum");
The MessageBox is for my testing purpose.
Now... The ColumnPlusLevel string can have very varied entry but it is always a repeated pattern starting with the plus sign.
i.e. "+MJ+MJ+MJ" or "+PPL14.1+PPL14.1+PPL14.1" as examples.
(It comes form Another software and I cant edit the output from that software)
How can I find out what that pattern is that is being repeated?
That in this exampels is the +-J10 or +MJ or +PPL14.1
In my case above I have tested it by using only a MessageBox to show the result but I want the repeated pattering stored in a string later on.
Maybe im doing it wrong by using Split, maybe there is another solution.
Maybe I use Split in the wrong way.
Hope you understand my problem and the result I want.
Thanks for any advice.
/Tomas

How can I find out what that pattern is that is being repeated?
Maybe i didn't understand the requirement fully, but isn't it easy as:
string[] tokens = ColumnPlusLevel.Split(new[]{'+'}, StringSplitOptions.RemoveEmptyEntries);
string first = tokens[0];
bool repeatingPattern = tokens.Skip(1).All(s => s == first);
If repeatingPattern is true you know that the pattern itself is first.
Can you maybe explain how the logic works
The line which contains tokens.Skip(1) is a LINQ query, so you need to add using System.Linq at the top of your code file. Since tokens is a string[] which implements IEnumerable<string> you can use any LINQ (extension-)method. Enumerable.Skip(1) will skip the first because i have already stored that in a variable and i want to know if all others are same. Therefore i use All which returns false as soon as one item doesn't match the condition(so one string is different to the first). If all are same you know that there is a repeating pattern which is already stored in the variable first.

You should use String.Split function :
string pattern = ColumnPlusLevel.Split("+")[0];

...but it is always a repeated pattern starting with the plus sign.
Why do you even need String.Split() here if the pattern always only repeats itself?
string input = #"+MJ+MJ+MJ";
int indexOfSecondPlus = input.IndexOf('+', 1);
string pattern = input.Remove(indexOfSecondPlus, input.Length - indexOfSecondPlus);
//pattern is now "+MJ"
No need of string split, no need to use LinQ

String has a method called Split which let's you split/divide the string based on a given character/character-set:
string givenString = "+-J10+-J10+-J10+-J10+-J10"'
string SplittedString = givenString.Split("+")[0] ///Here + is the character based on which the string would be splitted and 0 is the index number
string result = SplittedString.Replace("-","") //The mothod REPLACE replaces the given string with a targeted string,i added this so that you can get the numbers only from the string

Convert string into three letter Abbreviation

I've recently been given a new project by work to convert Any given string into 1-3 letter abbreviations.
An example of something similar to what I must produce is below however the strings given could be anything:
switch (string.Name)
{
case "Emotional, Social & Personal": return "ESP";
case "Speech & Language": return "SL";
case "Physical Development": return "PD";
case "Understanding the World": return "UW";
case "English": return "E";
case "Expressive Art & Design": return "EAD";
case "Science": return "S";
case "Understanding The World And It's People"; return "UTW";
}
I figured that I could use string.Split & count the number of words in the array. Then add conditions for handling particular length strings as generally these sentences wont be longer than 4 words however problems I will encounter are.
If a string is longer than I expected it wouldn't be handled
Symbols must be excluded from the abbreviation
Any suggestions as to the logic I could apply would be very appreciated.
Thanks

Something like the following should work with the examples you have given.
string abbreviation = new string(
input.Split()
.Where(s => s.Length > 0 && char.IsLetter(s[0]) && char.IsUpper(s[0]))
.Take(3)
.Select(s => s[0])
.ToArray());
You may need to adjust the filter based on your expected input. Possibly adding a list of words to ignore.

It seems that if it doesn't matter, you could just go for the simplest thing. If the string is shorter than 4 words, take the first letter of each string.
If the string is longer than 4, eliminate all "ands", and "ors", then do the same.
To be better, you could have a lookup dictionary of words that you wouldn't care about - like "the" or "so".
You could also keep an 3D char array, in alphabetical order for quick lookup. That way, you wouldn't have any repeating abbreviations.
However, there are only a finite number of abbreviations. Therefore, it might be better to keep the 'useless' words stored in another string. That way, if the abbreviation your program does by default is already taken, you can use the useless words to make a new one.
If all of the above fail, you could start to linearly move through string to get a different 3 letter word abbreviation - sort of like codons on DNA.

Perfect place to use a dictionary
Dictionary<string, string> dict = new Dictionary<string, string>() {
{"Emotional, Social & Personal", "ESP"},
{"Speech & Language","SL"},
{"Physical Development", "PD"},
{"Understanding the World","UW"},
{"English","E"},
{"Expressive Art & Design","EAD"},
{"Science","S"},
{"Understanding The World And It's People","UTW"}
};
string results = dict["English"];​

Following snippet may help you:
string input = "Emotional, Social & Personal"; // an example from the question
string plainText = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(Regex.Replace(input, #"[^0-9A-Za-z ,]", "").ToLower()); // will produce a text without special charactors
string abbreviation = String.Join("",plainText.Split(" ".ToCharArray(),StringSplitOptions.RemoveEmptyEntries).Select(y =>y[0]).ToArray());// get first character from each word

Best way to replace text in string

Looking for better algorithm / technique for replacing strings in a string variable. I have to loop through an unknown number of database records and for each one, I need to replace some text in a string variable. Right now it looks like this, but there has to be a better way:
using (eds ctx = new eds())
{
string targetText = "This is a sample string with words that will get replaced based on data pulled from the database";
List<parameter> lstParameters = ctx.ciParameters.ToList();
foreach (parameter in lstParameters)
{
string searchKey = parameter.searchKey;
string newValue = parameter.value;
targetText = targetText.Replace(searchKey, newValue);
}
}
From my understanding this is not good because I'm over writing the targetText variable, over and over in the loop. However, I'm not sure how structure the find and replace...
Appreciate any feedback.

there has to be a better way
Strings are immutable - you can't "change" them - all you can do is create a new string and replace the variable value (which is not as bad as you think). You could try using a StringBuilder as other suggest, but it's not 100% guaranteed to improve your performance.
You could change your algorithm to loop through the "words" in targetText, see if there's a match in parameters , take the "replacement" value and build up a new string, but I suspect the extra lookups will cost more than recreating the string value multiple times.
In any case, two important principles of performance improvement should be considered:
Start with the slowest part of your app first - you may see some improvement but if it does not improve the overall performance significantly then it doesn't matter that much
The only way to know if a particular change will improve your performance (and by how much) is to try it both ways and measure it.

StringBuilder will have less memory overhead and better performance, especially on large strings. String.Replace() vs. StringBuilder.Replace()
using (eds ctx = new eds())
{
string targetText = "This is a sample string with words that will get replaced based on data pulled from the database";
var builder = new StringBuilder(targetText);
List<parameter> lstParameters = ctx.ciParameters.ToList();
foreach (parameter in lstParameters)
{
string searchKey = parameter.searchKey;
string newValue = parameter.value;
targetText = builder.Replace(searchKey, newValue);
}
}

Actually, there is a better answer, assuming you're doing a large number of replacements. You can use a StringBuilder. As you know, strings are immutable. So as you said, you're creating strings over and over again in your loop.
If you convert your string to a StringBuilder
StringBuilder s = new StringBuilder(s, s.Length*2); // Adjust the capacity based on how much bigger you think the string will get due to replacements. The more accurate your estimate, the better this will perform.
foreach (parameter in lstParameters)
{
s.Replace(parameter.searchKey, parameter.value);
}
string targetString = s.ToString();
Now a caveat, if your list only has 2-3 items in it, this might not be any better. The answer to this question provides a nice analysis of the performance improvement you can expect to see.

C# Regex.Match to decimal

I have a string "-4.00 %" which I need to convert to a decimal so that I can declare it as a variable and use it later. The string itself is found in string[] rows. My code is as follows:
foreach (string[] row in rows)
{
string row1 = row[0].ToString();
Match rownum = Regex.Match(row1.ToString(), #"\-?\d+\.+?\d+[^%]");
string act = Convert.ToString(rownum); //wouldn't convert match to decimal
decimal actual = Convert.ToDecimal(act);
textBox1.Text = (actual.ToString());
}
This results in "Input string was not in a correct format." Any ideas?
Thanks.

I see two things happening here that could contribute.
You are treating the Regex Match as though you expect it to be a string, but what a Match retrieves is a MatchGroup.
Rather than converting rownum to a string, you need to lookat rownum.Groups[0].
Secondly, you have no parenthesised match to capture. #"(\-?\d+\.+?\d+)%" will create a capture group from the whole lot. This may not matter, I don't know how C# behaves in this circumstance exactly, but if you start stretching your regexes you will want to use bracketed capture groups so you might as well start as you want to go on.

Here's a modified version of your code that changes the regex to use a capturing group and explicitly look for a %. As a consequence, this also simplifies the parsing to decimal (no longer need an intermediary string):
EDIT : check rownum.Success as per executor's suggestion in comments
string[] rows = new [] {"abc -4.01%", "def 6.45%", "monkey" };
foreach (string row in rows)
{
//regex captures number but not %
Match rownum = Regex.Match(row.ToString(), #"(\-?\d+\.+?\d+)%");
//check for match
if(!rownum.Success) continue;
//get value of first (and only) capture
string capture = rownum.Groups[1].Value;
//convert to decimal
decimal actual = decimal.Parse(capture);
//TODO: do something with actual
}

If you're going to use the Match class to handle this, then you have to access the Match.Groups property to get the collection of matches. This class assumes that more than one occurrence appears. If you can guarantee that you'll always get 1 and only 1 you could get it with:
string act = rownum.Groups[0];
Otherwise you'll need to parse through it as in the MSDN documentation.